How to manipulate strings in Slack Workflows

How can we manipulate strings in Slack workflows?

The primary use case is to extract URLs from previous workflow steps which inconveniently return them within a string.

For example: Here is the url! https://... Have fun!

I just want the https://... part, so that I can format the message more nicely. Because links can be very long & ugly, and it would be better to display them as a simple link.

I ended up doing this by using custom functions/steps for workflow apps.

It's basically JavaScript/TypeScript code running in a secure Deno sandbox on Slack's own infrastructure, and it's pretty easy to setup once you wrap your head around it.

• Here's a quickstart guide which is useful to get started quickly.
• And here's a quick reference for the Slack CLI commands.

Here's the code for the function to extract a URL from some text:

import { DefineFunction, Schema, SlackFunction } from "deno-slack-sdk/mod.ts";

export const ExtractUrlDefinition = DefineFunction({
  callback_id: "extract_url",
  title: "Extract URL",
  description: "Extracts a URL from some text",
  source_file: "functions/extract_url.ts",
  input_parameters: {
    properties: {
      text: {
        type: Schema.types.string,
        description: "The string in which to find & extract the URL",
      },
    },
    required: ["text"],
  },
  output_parameters: {
    properties: {
      url: {
        type: Schema.types.string,
        description: "The extracted URL (if one was found)",
      },
    },
    required: ["url"],
  },
});

export default SlackFunction(
  ExtractUrlDefinition,
  ({ inputs }) => {
    const url = inputs.text.match(/http[^ ]+/)?.[0] || "";

    return { outputs: { url } };
  },
);